It has been well established that children with low MAs--both retarded children and young nonretarded children--have difficulty mastering complex relational tasks such as oddity and match to sample. The present proposal details a series of studies designed to demonstrate the facilitation of what we refer to as adaptive attending behavior. In the context of relational learning, attention is adaptive when if facilitates the learning of a relevant stimulus complex rather than merely the discrimination of a discrete stimulus dimension, configuration or position. Paradigms to be utilized include oddity, match to sample, span of apprehension, and stimulus duration. Manipulations of stimulus familiarity as a means of facilitating relational learning are a component of each study. Previous research by the present investigators has provided evidence of the theoretical and practical significance of perceptually based manipulations in inducing rapid discrimination learning with young, developmentally delayed children who are similar in chronological age and intellectual functioning to the children who will participate in the proposed series of studies